feature request: git format-patch - allow --suffix to work with --numbered-files

"Numbered files" is good for creating patches with uniform filenames, rather
than verbose filenames containing part of the commit message, but if working for
example with submodules, there is possible name collision if pooling the patches
in one place.

I thought that --suffix=$name would be a good way to disambiguate but found that
--numbered-files wins and kills any suffix.

Hence suggestion that --suffix used with --numbered-files is allowed to generate
a filename suffix as it does when not in "numbered files" mode.

In the absence of a --suffix command, the behaviour would be as now.